Site Conversion Warnings

I'm migrating a Dev platform from a Win 32-bit/ AGS V10 VM to a 64-bit/AGS V10.1 VM.

Installed V10.1 AGS & installed the same GE  3.15 & SL 1.10 versions, then copied the sites folder. I'm able to open the sites, repoint to the newly created / local map services and the viewers seems to work with 3 sites I've migrated...

Yet, in GE Manager, each of the sites show the warning icon next to 'Configure Site' and reports "Site may not function properly." & "The xxx ArcGIS Map Service appears to be offline." The logs display the same info, but doesn't seem to add anything more intelligable.

I've used the aforementioned method with another DEV->PRD scenario and not encountered this issue.

As a test, I deleted one of the easily replacable sites, and rebuilt it. It does not display the warning. The challenge is that 1 of the sites (displaying the warning) is the base site referenced by most others, and another has a very large number of layers. Each of these have a large amount of configuration/ non-default settings applied, so rebuilding them would be time consuming.

Any insights and guidance on this "error"?

Thanks!